Critical concentration in etching doped poly silicon with HF/HNO3

Abstract

In some embodiments, the present invention discloses an etchant solution hydrochloric acid and nitric acid to etch doped polysilicon at low etch rates. The doped polysilicon can be doped with Ge, In, B and Ga. Preferably, the concentration of hydrochloric acid can be greater than 1 vol %, and the concentration of nitric acid is greater than 15 vol %.

What is claimed: 
     
       1. A method to etch doped polysilicon comprising
 providing a doped polysilicon layer on a substrate; 
 applying an etchant solution on the doped polysilicon layer, wherein the etchant solution consists of dilute nitric acid and dilute hydrofluoric acid, 
 wherein the concentration of nitric acid is greater than 10 vol % and less than 30 vol %, 
 wherein the concentration of hydrofluoric acid is greater than 1 vol % and less than 5 vol %, and 
 wherein the doped polysilicon layer comprises dopants of Ge, In, B and Ga. 
 
     
     
       2. A method as in  claim 1  wherein the concentration of nitric acid is greater than 15 vol %. 
     
     
       3. A method as in  claim 1  wherein the doped polysilicon layer further comprises one or more dopants selected from a group consisting of Al, P, N, and Sb. 
     
     
       4. A method as in  claim 1  wherein at least one dopant concentration of the doped polysilicon layer is less than 1×10 18  atoms/cm 3 . 
     
     
       5. A method to etch doped polysilicon comprising
 providing a doped polysilicon layer on a substrate; and 
 applying an etchant solution on the doped polysilicon layer, wherein the etchant solution consists of dilute nitric acid and dilute hydrofluoric acid, 
 wherein the etchant solution etches doped polysilicon at an etch rate less than 20 nm/min, 
 wherein the concentration of nitric acid is greater than 10 vol %, 
 wherein the concentration of hydrofluoric acid is greater than 1 vol %, and 
 wherein the doped polysilicon layer comprises dopants of Ge, In, B, and Ga. 
 
     
     
       6. A method as in  claim 5  wherein the concentration of nitric acid is greater than 15 vol %. 
     
     
       7. A method as in  claim 5  wherein the concentration of nitric acid is less than 30 vol %. 
     
     
       8. A method as in  claim 5  wherein the concentration of hydrofluoric acid is less than 5 vol %. 
     
     
       9. A method as in  claim 5  wherein the doped polysilicon layer further comprises one or more dopants selected from a group consisting of Al, P, N, and Sb. 
     
     
       10. A method as in  claim 5  wherein at least one dopant concentration of the doped polysilicon layer is less than 1×10 18  atoms/cm 3 . 
     
     
       11. A method to etch doped polysilicon comprising
 providing a doped polysilicon layer on a substrate; and 
 applying an etchant solution on the doped polysilicon layer, wherein the etchant solution consists of dilute comprising nitric acid and dilute hydrofluoric acid on the doped polysilicon layer, 
 wherein the etchant solution etches doped polysilicon at an etch rate less than 20 nm/min, 
 wherein the etchant solution etches doped polysilicon at an etch rate greater than 0.05 nm/min, and 
 wherein the doped polysilicon layer comprises dopants of Ge, In, B, and Ga. 
 
     
     
       12. A method as in  claim 11  wherein the concentration of nitric acid is greater than 15 vol %. 
     
     
       13. A method as in  claim 11  wherein the concentration of nitric acid is less than 30 vol %. 
     
     
       14. A method as in  claim 11  wherein the concentration of hydrofluoric acid is greater than 1 vol %. 
     
     
       15. A method as in  claim 11  wherein the concentration of hydrofluoric acid is less than 5 vol %. 
     
     
       16. A method as in  claim 11  wherein the doped polysilicon layer further comprises one or more dopants selected from a group consisting of Al, P, N, and Sb. 
     
     
       17. A method as in  claim 11  wherein at least one dopant concentration of the doped polysilicon layer is less than 1×10 18  atoms/cm 3 .